The functions of transmission devices such as Layer 2 switches and communication lines contained therein have become diversified with an increase in demand for communication, and monitoring control performed within transmission devices has become complex. The transmission devices each include, for example, transmission processing units that each perform transmission processing for a main signal, a control unit that performs monitoring control of each transmission processing unit, and so forth. In addition, the main signal is contained in, for example, an Ethernet (registered trademark, the same shall apply hereafter) frame or the like.
The control unit performs, for example, various kinds of setting processing operations on the transmission processing units, and collects pieces of information indicating various kinds of alarms from the transmission processing units. The control unit is connected to a network management device that manages individual transmission devices within a network, through a local area network (LAN) or the like.
An administrator of the network manages a plurality of transmission devices by operating the network management device. In order to identify a failure factor, the network management device collects various kinds of logs from, for example, the control units in the respective transmission devices, and collects communication states (error rates or the like) of communication lines. Therefore, in a case where a failure occurs in the control unit within one of the transmission devices, it becomes difficult to manage the corresponding transmission device, and a problem is caused in the operation of the network.
In order to avoid such a situation, the transmission devices each have the redundant configuration of the control unit. In other words, in each of the transmission devices, two systems of a control unit of an operational system and a control unit of a backup system are provided. Accordingly, in a case where a failure occurs in the control unit of the operational system, the control unit of the backup system monitors and controls the individual transmission processing units, on behalf of the control unit of the operational system in which the failure occurs. In addition, as examples of the failure in the control unit, a failure in a processor such as an embedded central processing unit (CPU) (CPU Halt is included) and communication failures with the network management device and one of the transmission processing units are cited.
For example, in Japanese Laid-open Patent Publication No. 2004-336658, in regard to the monitoring control of the transmission devices, a point that a change in the state information of a port transmitted from a node adjacent to a node of a failure occurrence is detected and the node of a failure occurrence is identified based on connection relationship information between network elements has been disclosed. In addition, in Japanese Laid-open Patent Publication No. 2000-250624, a point that, within a communication control device, a control unit monitors the states of other individual units has been disclosed.